In 1983, in U.S. Pat. No. 4,395,285, Merkert taught a low density, porous compact of prepared mix containing silica fume, finely-divided carbonaceous reducing agents such as petroleum coke or coal, and optimally with iron and a binder.
In 1987, U.S. Pat. No. 4,701,214, Midrex taught reduction by utilizing off gas generated by a smelting furnace in a rotary hearth furnace. A method of operation was promoted which required less energy and a smaller smelting furnace by introducing gaseous reductants and fuel into the rotary hearth furnace.
In 1987, in U.S. Pat. No. 4,731,112, Hoffman taught a method of making a molten ferroalloy product in a melting furnace from a feed briquette of metallized iron, granulated alloy metal oxide, and a carbonaceous material.
In 1998, in U.S. Pat. No. 5,730,775, Midrex taught an improved method known by the trade name or trademark of FASTMET, and apparatus for producing direct reduced iron from iron oxide and iron bearing and carbon compacts that are layered no more than two layers deep onto a rotary hearth, and are metallized by heating the compacts to temperatures of approximately 1316.degree. to 1427.degree. C., for a short time period. For a general understanding of the recent art, U.S. Pat. No. 5,730,775 is incorporated herein by reference.
All major steelmaking processes require the input of iron bearing materials as process feedstocks. In a steelmaking process utilizing a basic oxygen furnace, the iron bearing feed materials are usually blast furnace hot metal and steel scrap. A broadly used iron source is a product known as Direct Reduced Iron ("DRI") which is produced by the solid state reduction of iron ore or iron oxide to metallized iron without the formation of liquid iron. Metallized in this sense, and throughout this specification, does not mean coated with metal, but means substantially reduced to the metallic state.
Improvements are sought within the industry for furnace modifications and improved methods of operation that provide for efficient, continuous production of high purity iron with a range of carbon content in which iron oxides are efficiently reduced to purified iron in the process while slag components are separated from the purified iron.
Specifically, a high purity iron product with a specified range of carbon content, a specified range of silicon and manganese content, and low sulfur and low phosphorous content is sought by the steelmaking industry. Molten iron product of this quality is typically produced by a blast furnace or conditioned after blast furnace production. Other melters such as conventional electric arc furnaces or submerged arc furnaces produce molten iron having different chemistry, in which the preferred reduced silicon content is not achieved efficiently. The reason that alternative melters cannot meet the industry's chemistry requirements for hot metal is that these furnaces fail to provide the necessary simultaneous conditions of optimum thermodynamic process equilibrium, and rapid melting. The invented method provides the environment as well as the process flexibility such that the desired silicon content in the hot metal can be easily achieved (increased or decreased) by adjusting power input to the electric melter (temperature).